Arrangement and method for turning a propulsion unit

ABSTRACT

A propeller drive arrangement for moving and steering a vessel traveling in water. The propeller drive arrangement includes an azimuthing propulsion unit, a power supply, a control unit, and a sensor means. An operating means is provided for turning the azimuthing propulsion unit it relation to the hull of the vessel for steering the vessel in accordance with a steering command controlled by the vessel&#39;s steering control device. The operating means also includes a second electric motor for turning the azimuthing propulsion unit via a mechanical power transmission that is connected to the second electric motor. The sensor means is connected to the control unit and used for detecting the rotational position of the azimuthing propulsion unit. The control unit is configured so that both the steering command information originating from the steering control device and the rotational position information originating from the sensor means can be processed.

THE FIELD OF THE INVENTION

The invention relates to a propeller drive arrangement for vessels usedin water transport, and in particular to an arrangement whichincorporates a propulsion unit which can be turned in relation to thehull of the vessel. The present invention also relates to a method formoving and steering a vessel travelling on water.

THE BACKGROUND TO THE INVENTION

In most cases, various ships or the like vessels (such as passengerships and ferries, cargo vessels, lighters, oil tankers, ice-breakers,off-shore vessels, military vessels etc.) are moved by means of thepropulsion or draw created by a rotatable propeller or severalpropellers. Vessels have been steered using separate rudder gear.

Traditionally, propeller operating, i.e., rotation arrangements haveinvolved a propeller shaft drive, such as a diesel, gas or electricengine, being positioned inside the hull of the vessel, from where thepropeller shaft has been taken via a duct sealed to make it watertightto outside the hull of the vessel. The propeller itself is located atthe other end, i.e., the end extending outside the vessel, of thepropeller shaft which is connected either directly to the engine or to apossible gearing. This solution is employed in the majority of all thevessels used in water transport in order to obtain the force requiredfor movement.

Recently, one have also arranged for fitting vessels with propellerunits in which the equipment (usually an electric motor) creating thepropulsion power for the propeller shaft and any gearing are positionedoutside the hull of the vessel within a special chamber or pod supportedfor rotating in relation to the hull. This unit can be turned inrelation to the hull, which means that it can also be used for steeringthe vessel instead of separate rudder gear. More precisely, the podcontaining the engine is supported by means of a special tubular or thelike shaft to rotate in relation to the hull of the ship, which tubularshaft has been arranged through the bottom of the ship. This kind ofpropulsion unit is disclosed in greater detail in, inter alia, theApplicant's FI Patent No. 76977. These units are also referred togenerally as azimuthing propulsion units, and, e.g., the applicant inthe present application provides azimuthing units of this kind under thetrademark AZIPOD.

Besides the advantages obtained by the omitting of a long propellershaft and separate rudder gear, this equipment has also been found toachieve a fundamental improvement in the vessel's steerability. Thevessel's energy economy has also been found to improve. The use ofazimuthing propulsion units in a variety of vessels designed for watertransport has in fact become more common over the last few years, and itis assumed that their popularity will continue to grow.

In known solutions, the azimuthing propulsion unit's turning arrangementhas generally been implemented so that a geared tiller ring or the liketiller rim has been attached to the tubular shaft which forms the unit'sswivelling axis, which tiller is rotated with the aid of hydraulicengines adapted to co-operate with it. The turning movement of thetiller is also halted and kept in the halted position whenever nosteering movements are performed by means of the same hydraulic engines.For this reason, there is always normal operating pressure in thehydraulic system, also when the vessel runs straight.

In accordance with one known solution, four hydraulic engines have beenpositioned in connection with the turning rim. The operating machinerywhich creates the hydraulic pressure required in the engines comprisesof a hydraulic pump and of an electric motor which rotates it. In orderto enhance the service reliability of the turning gear, the hydraulicengines can be arranged in two separate hydraulic circuits, each ofwhich has its own operating machinery to create the hydraulic pressure.

A hydraulic turning system has been employed, inter alia, becausehydraulics readily allow the relatively high torque required for turningan azimuthing propulsion unit to be obtained at a relatively low speedof rotation. At the same time, the turning and steering of the vessel bymeans of the hydraulics can be readily and relatively preciselycontrolled with the aid of traditional valve gears and correspondinghydraulic components. As was already stated earlier, one featureobtained with a hydraulic system has been the fact that it enables theturning movement of the propulsion unit's shaft to be halted quickly andprecisely in the desired position. This position can then be maintained,something which has been regarded as quite essential for the steering ofthe vessel.

SUMMARY OF THE INVENTION

However, a number of problems and deficiencies have been observed in theknown hydraulic solution, which is as such found to be effective andreliable. In order to implement the turning system, the vessels have tobe fitted with an expensive and complicated separate hydraulic systemincorporating a large variety of components despite the fact that therotation of the propeller itself is performed by means of an electricmotor. This means, inter alia, that some of the benefit in efficiency ofthe use of space, obtained with the outboard azimuthing propulsion unit,is lost. Hydraulic systems also require regular and relatively frequentmaintenance and inspections, which give rise to costs, and may even callfor the vessel to be withdrawn from service for the duration of themaintenance work. Another deficiency of the hydraulic systems has beenthe fact that they have a known tendency to leak/drip oil or similarhydraulic fluid into their surroundings, in particular from hose pipesand various joints and sealing surfaces. Apart from the costs arisingfrom the leakage and consumption of hydraulic fluid, this also causes anenvironmental and cleanliness problem. Leaks also cause a considerablesafety risk, since surfaces stained by hydraulic fluid become slipperyand thereby dangerous, and leaked hydraulic fluid may also constitute afire risk. The hydraulic system's internal pressure is relatively high,and thereby, e.g., a leak in a hose pipe may cause a high-pressure andoften aciform (needle-shaped) jet of oil, which may cause seriousinjuries if it impacts with operating personnel. While it is running,the hydraulic system is also noisy, and this affects, inter alia, theoperating personnel's working conditions. The noise is continuous, sincethe system should be on all the time when the vessel is moving. Further,the hydraulic system achieves only a constant-speed turning movement(i.e., single-speed) for the propulsion unit. However, there aresituations where a possibility for at least one other turning speedwould be desirable.

The purpose of the present invention is to eliminate the deficiencies ofthe known technology and create a new kind of solution for turning anazimuthing propulsion unit in relation to the hull of a vessel.

One objective of the present invention is to achieve a solution whichavoids the use of a separate hydraulic system and the associatedproblems in the turning of an azimuthing propulsion unit.

One objective of the present invention is to achieve a solution whichimproves the reliability and overall economy of an azimuthing propulsionunit's turning machinery compared to the known solutions.

One objective of the present invention is to obtain a solution whichreduces the noise level of an azimuthing propulsion unit's turningmachinery compared to the known solutions.

One objective of the present invention is to achieve a solution whichallows the turning speed of an azimuthing propulsion unit to be alteredand/or adjusted.

Another objective of the present invention is to obtain a solution whichreduces the environmental risk caused by the turning machinery andimproves its general level of cleanliness and safety compared to knownsolutions.

The invention is based on the basic insight that an azimuth propulsionunit is rotated by a direct electric drive which is controlled by acontrol unit that is adapted to deal with both steering commands issuedfor the vessel and position information provided by a sensor devicewhich detects the position of the azimuthing propulsion unit. Theoperation of the electric motor is controlled by controlling theelectric motor's power supply unit using the control unit on the basisof this processing.

More precisely, the arrangement according to the present invention ischaracterized in particular by what is disclosed in the characterizingsection of the enclosed independent claim 1. The method according to thepresent invention is characterized by what is disclosed in thecharacterizing section in the enclosed independent claim 6.

In accordance with one advantageous embodiment of the invention, thepower transmission equipment which turns the azimuthing propulsion unitcomprises a gear rim fitted to the shaft unit, a pinion gear, a worm, orthe like adapted to co-operate with said gear rim, which gear wheel isrotated via a reduction gearing connected to an electric motor.Favorably, the equipment further comprises a suitable brake means forhalting the turning of the azimuthing propulsion unit and maintainingthe halted position and a functional connection between said brake meansand said control unit for transferring control commands for said brakemeans. In accordance with one preferred embodiment the speed of rotationof the electric motor is regulated by means of an AC inverter drive.

The present invention provides several significant benefits. By means ofthe invention it is possible to replace the known arrangement based onthe use of hydraulics, and thus the aforesaid problems associated withthe use of hydraulics can be eliminated. The overall economy of asolution based on the use of an electric motor is good, and themaintenance requirement almost nonexistent. A turning system based on anelectric drive is also highly reliable. In modern vessels, electricityis readily available and is employed in a number of different places(also the azimuthing propulsion unit incorporates an electric motor),and so the construction of a separate (expensive) hydraulic system isavoided. An electric drive can be used to achieve a turning arrangementwith adjustable speeds for the azimuthing propulsion unit.

The present invention and its other aspects and benefits are describedin greater detail in the following exemplary presentation and referringalso to the attached drawing in which corresponding reference numbers inthe separate Figures refer to corresponding features.

A BRIEF EXPLANATION OF THE DRAWINGS

FIG. 1 shows a simplified diagrammatic visualization of one embodimentof the present invention,

FIG. 2 shows a block diagram for the arrangement according to FIG. 1,

FIG. 3 shows a propeller unit installed in a ship,

FIG. 4 shows turning equipment according to one alternative in the formof a diagrammatic visualization, and

FIG. 5 shows a flow diagram for the operation of the turning arrangementaccording to the invention.

A DETAILED EXPLANATION OF THE DRAWINGS

FIG. 1 discloses in the form of a diagrammatic plan in principle andFIG. 2 in the form of a block diagram one embodiment of a turningmachinery according to the present invention. FIG. 3 discloses anazimuthing propulsion unit 6 installed in a vessel 9. More precisely,FIG. 1 discloses a azimuthing propulsion unit 6, which comprises awatertight pod 1. Installed inside said pod 1 is an electric motor 2,which can be any kind of known electric motor structure. Said electricmotor 2 is connected via a shaft 3 to a propeller 4 in a manner knownper se.

According to one alternative, the structure can be fitted with a gear insaid pod 1 between said electric motor 2 and said propeller 4. Inaccordance with one alternative, there is more than one propeller foreach pod. In that case, there can be, e.g., two propellers, one at thefront of the pod and one at the rear.

Said pod 1 is supported, for rotation around the vertical axis, at thehull of the vessel (the hull is not shown, see e.g., FIG. 3) by means ofan essentially vertical shaft means 8 (the bearings are not shown in theFigure, one alternative for this is shown, e.g., in the cited FI Patent76977, which is included herein by reference). Said shaft means 8 (e.g.,a hollow tubular shaft) can, e.g., have a diameter which allows formaintenance of the motor located down in the pod, a possible gearing andthe propeller shaft.

A 360° gear rim 10 or a corresponding tiller rim is connected to saidshaft means 8 for transferring, to said shaft means 8, the powerrequired for turning the shaft means n relation to the hull of thevessel. When the shaft means 8 is turned, said azimuth propulsion unit 8turns correspondingly. In the FIG. 1 case, a turning machinery 40 forsaid gear rim 10 comprises a pinion gear 12, a bevel gear 14, a switch24 a gearing 22 and an electric motor 20, and the shafts between these.Also shown is a brake means arranged at said shaft 21, which means inthis case consists of a disc brake 26 and drive equipment requiredtherefore. It should be observed that not all the aforesaid elements arenecessary in the turning machinery for implementing the presentinvention but that some of them can be omitted or replaced with otherelements.

The driving power for electric motor 20 is fed from an AC inverter 30,which acts as the power source, via a conductor 28. The operatingprinciple of the AC inverter is a technology known to a person skilledin the art, and so there is no need to explain it here apart fromstating that the general main components of the AC inverter are arectifier, a direct voltage intermediate circuit and a inverterrectifier (=inverter component). AC inverters are generally usednowadays, inter alia, as input devices for alternating-current motors,and they are particularly advantageous in various controllableelectrical drives. The most commonly employed AC inverters include PWMinverters based on pulse width modulation and fitted with a voltageintermediate circuit.

An AC inverter is advantageous to use, inter ali , because it provides aregulation of the rotational speed of a said turning machinery 40 andthereby of the rotational speed of said shaft 8. In accordance with onesolution, there are at least two different speeds in use. In accordancewith another solution, the rotational speed can be regulated within apredefined speed range, such as from 0 to the nominal speed of rotation.

The operation of said AC inverter 30 is controlled by a control unit 34(such as servo steering) via a connection 32. Said control unit 34 is inturn connected functionally to a steering control device located on thebridge or in a similar position, such as a helm wheel 38, which is useto issue the actual steering commands for the vessel. Steering commandsissued manually using the helm are converted, e.g., by means of aseparate analogue servo means into course commands. According to anothersolution, the steering commands are converted using a transformerconnected to the wheel into digital steering signals, which are sent viaa connection 36 to the control unit.

Said control unit 34 uses the steering command information given by thehelm 38 to control the AC inverter 30, which in turn supplies current tothe motor 20, whose desired (course, speed) rotation clock- oranti-clockwise generate the desired change in the turning angle of saidshaft 8 and thereby of the propulsion unit 6.

Control unit 34 can be any kind of suitable data-processing deviceand/or control device such as a microprocessor, a servo steering means(such as a so-called analogue servo) or a corresponding device which isable to perform the processing of steering commands and otherinformation affecting the steering and presented later, and to controlthe AC inverter or similar power unit on the basis of this processing.

FIGS. 1 and 2 also show a position or angle sensor 16 arranged inconnection with the azimuthing propulsion unit 6 (here on top of gearrim 10) to detect the turning angle of said shaft 8. Various positionsensors suitable or this purpose are known per se, and said positionsensor 16 can be based, e.g., on a photo-optic sensor, a so-calledsin/cos sensor or on a sensor based on machine or computer visionsystems which defines the turning angle. It should be observed that thetype of sensor 16 has no fundamental effect on the implementation of theinvention, but that what essential is to define the direction of theazimuthing propulsion unit reliably by means of the sensor device used.

Position sensor 16 has a functional connection 18 to control unit 34 forthe purpose of transmitting position signals. Said connection 18 can be,e.g., a cable connection or a radio link. The arrangement can alsocomprise an analogue/digital (A/D) converter 35 for converting ananalogue position signal from sensor 16 into a digital format which canbe processed by said control unit 34, if the control unit used requiressuch conversion.

Control unit 34 is arranged to combine, in a processor or the likeprocessing device 33, the information it has received from said positionsensor 16 with the steering commands obtained from said steering controldevice 38, and to control the operation of said AC inverter 30 or thelike power supply unit on the basis of this processing, as shown in FIG.2.

FIGS. 1 and 2 also show said brake means 26, as presented above. It isarranged to halt the turning movement of the propulsion unit in adesired position and to old the propulsion unit in a fixed positionwhenever no steering commands have been issued. The operation of saidbrake means 26 (such as the timing and force of braking and holding) canbe controlled via the functional connection by means of the control unitwhich controls the operation of the system. According to the favorablesolution shown in FIG. 2 the operation of said brake means 26 iscontrolled by said AC inverter 30, which in turn receives the steeringcommands from control unit 34. The braking arrangement also allows theinformation originating from position sensor 16 to be utilized in thecontrol of the braking, so that the direction of the propeller, i.e., ofthe propulsion force which moves the vessel, can be adjusted toprecisely correct.

The brake means can be implemented, e.g., in the form of a mechanicalfriction brake (such as disc or drum brakes, brake shoes) or of amagnetic brake, which can be positioned in a suitable part of the powertransmission equipment 40, or even directly to brake/hold said shaftmeans 8 of the propulsion unit 6. In accordance with one alternative,said gearing 22 or the cogging affecting said gear rim 10 is selected sothat it brakes against the rotating movement emanating from thepropeller unit 6, but allows a rotation emanating from said motor 20,i.e., it is of a type which allows turning power from only one directionto be carried forward.

Yet another possibility is to use said electric motor 20 forbraking/holding. In this case, the output of the motor 20 is controlled,e.g., using said AC inverter 30 and said control unit 34 so that thedesired braking/holding effect is obtained in a desired and controlledmanner. By means of the electric motor 20 a either full braking/holdingcan be obtained or it can be used to generate only some of the requiredbraking power, in which case the braking is completed by means of aseparate brake means. In accordance with this embodiment it is possibleto lighten/reduce the braking force required from a mechanical brake inthe braking. In accordance with one solution, said electric motor 20 isused during braking as a generator, and the electrical energy therebygenerated during the braking is fed into the electricity network. Theelectricity network is advantageously the same as the one from which theelectric machine in the turning system 40 takes its operating power whenit functions as an electric motor.

FIG. 4 shows a solution which aims for the most compact and simplestructure possible. In accordance with FIG. 4, said turning gear rim 10is rotated by means of a worm 12 connected directly to said gearing 22.However, in this connection, attention is drawn to the point thatalthough the solutions in FIGS. 1 and 4 show a gear rim 10 and aco-operating rotating means 12, the use of a gear rim is not alwaysnecessary and it can also be replaced with another solution whichpermits power transmission to the shaft unit 8 of said propulsion unit6. A solution of this kind is, e.g., a rim motor, which means anelectric motor having an essentially large stator coil arranged at therim of said shaft 8. In this case, the power transmission machinery isconsidered to consist of any means transferring the power from saidmotor to said shaft 8.

FIG. 4 also shows a sensor solution which employs non-contacting sensor16 installed near to but, nonetheless, separately from the propulsionunit's shaft means. Said sensor 16 detects position markings arrangedaround the shaft unit, and produces a position signal on the basis ofthis detected information.

FIG. 5 shows a flow diagram for the operation of a turning equipmentaccording to the present invention. In accordance with the principles ofthe invention, the vessel is moved by means of the azimuthing propulsionunit. The position of the azimuthing propulsion unit is detected bymeans of a sensor device. The information provided by the sensor devicecan be utilized in either analogue format or it can if necessary beconverted into digital format. Unless a new command has been issued foraltering the course, the position of the azimuthing propulsion unit iskept in the most recent position issued from the bridge. If theobservation of position information indicates a need to correct theposition (deviation from course given, brake slipped or other similarreason), this can be performed automatically.

When the vessel has to be turned, the corresponding command is issued tothe control unit. The command is processed in a pre-defined manner inthe control unit, also utilizing the latest position informationobtained from the sensor. After said processing, the control unit issuesa command to the azimuthing propulsion unit's turning machinery, whichcomprises said electric motor. The electric motor is controlled bycontrolling the operation of the power source, such as an inverter,after which the desired rotation of the electric motor causes theazimuthing propulsion unit to turn as required via the mechanicaltransmission of the turning machinery, and the vessel alters its coursecorrespondingly.

Thus, the present invention provides a device and method which provide anew kind of solution for steering a vessel fitted with an azimuthingpropulsion unit. The solution avoids a number of the deficiencies in theprior art and brings the benefit of a simpler structure, better overalleconomy, and operating comfort and safety. It should be observed thatthe above exemplifying embodiments of the present invention do notrestrict the scope of protection for the invention as disclosed in theclaims, but that the claims are intended to cover all adaptations,equivalences and alternatives which fall within the invention's spiritand scope as defined in the appended claims.

What is claimed is:
 1. A propeller drive arrangement for moving andsteering a vessel traveling in water, which arrangement comprises: anazimuthing propulsion unit (6), which comprises a pod (1) positionableoutside said vessel below sea level, a first electric motor (2)positioned inside said pod, for rotating a propeller (5) connected tosaid pod, and a shaft means (8) connected to said pod for supportingsaid pod in a rotatable manner from a hull of said vessel (9), operatingmeans for turning said azimuthing propulsion unit (6) in relation tosaid hull of said vessel (9) for steering said vessel in accordance witha steering command originating from a vessel's steering control device(38), characterized in that said operating means comprises a secondelectric motor (20) for turning said azimuthing propulsion unit (6) viaa mechanical power transmission equipment (40) connected to said secondelectric motor, the arrangement further comprising a power supply unit(30) for supplying electric power to said second electric motor (20), acontrol unit (34) for controlling the operation of said second electricmotor by controlling said power supply unit (30), a sensor means (16)functionally connected (18) to said control unit (34) for detecting therotational position of said azimuthing propulsion unit (6), said controlunit (34) being, arranged for processing both a steering commandinformation originating from said steering control device (38) androtational position information originating from said sensor means (16)and to control the operation of the second electric motor (2) on thebasis of said processing.
 2. A propeller drive arrangement as defined inclaim 1, characterized in that a power transmission equipment comprisesa 360° gear rim (10) arranged at said shaft means, a pinion gear or wormarrangement (12) arranged for co-operation with said gear rim, and agearing (22) arranged between said arrangement and said second electricmotor (20).
 3. A propeller drive arrangement as defined in claim 1,characterized in that said power supply unit (30) comprises an ACinverter.
 4. A propeller drive arrangement as defined in claim 3,characterized in that it comprises a brake means (26), and a functionalconnection between said brake means and said AC inverter fortransferring control commands to the brake means (26).
 5. A propellerdrive arrangement as defined in claim 4, characterized in that saidbrake means is a brake distinct from said second electric motor.
 6. Apropeller drive arrangement as defined in claim 5, wherein the brakemeans is a friction brake.
 7. A propeller drive arrangement as definedin claim 5, wherein the brake means is a magnetic brake.
 8. A method formoving and steering a vessel traveling in water, in which method saidvessel (9) is moved using an azimuthing propulsion unit (6) comprising apod (1) positioned outside said vessel below sea level, a first electricmotor (2) positioned within said pod for rotating a propeller (4)arranged at said pod, and a shaft unit (8) connected to said pod forsupporting, in a rotatable manner, said pod to the hull of said vessel(9), said azimuthing propulsion unit (6) is turned in relation to saidhull of said vessel (9) for steering the vessel in accordance with asteering command given by the vessel's steering control device (38),characterized in detecting a rotational position of the azimuthingpropulsion unit (6) by means of a sensor means (16) connectedfunctionally (18) to a control unit (34), processing, in said controlunit (34), steering command information from said control device (38)and rotational position information from said sensor means (16), turningsaid azimuthing propulsion unit (6) by means of a mechanical powertransmission machinery connected to a second electric motor (20) on thebasis of said processing performed in said control unit (34), andsupplying electric power to said second electric motor (20) in responseto said processing performed by said control unit (34).
 9. A method asdefined in patent claim 8, characterized in turning said azimuthingpropulsion unit (6) by means of a joint operation of a 360° gear rim(10), a pinion gear or a worm arrangement (12) arranged to co-operatewith said gear rim and a gearing (22) arranged between said arrangementand said second electric motor (20).
 10. A method as defined in claim 8,characterized in supplying electric power for said second electric motorvia an AC inverter, and regulating, in a required manner, a turningspeed of said azimuthing propulsion unit (6) by a correspondingregulation of the electric supply provided by said AC inverter.
 11. Amethod as defined in claim 10, characterized in halting the rotation ofsaid azimuthing propulsion unit (6) by means of a brake device (26)controlled by said AC inverter (30).
 12. A method as defined in claim10, characterized in maintaining the turning position of said azimuthingpropulsion unit (6) by means of a brake device (26) controlled by an ACinverter (30).
 13. A method as defined in claim 8, characterized inprocessing said steering command and said position information in saidcontrol unit by means of a data-processing device.
 14. A method asdefined in claim 13, wherein the data-processing device is amicroprocessor.
 15. A method as defined in claim 13, wherein thedata-processing device is a power control unit.
 16. A method as definedin claim 8, characterized in braking the rotation of said azimuthingunit by means of an electric generator, and feeding the electric energygenerated into the electricity network.